Q: Since whales, porpoises, dolphins, manatees and other
fully aquatic marine mammals are air breathers, don't they all (the ones that
don't get killed) eventually drown? They can't swim forever, and the ones that
aren't taken by predators don't just die... or can they hold their breath until
they die? I've never gotten a good, complete answer to this question from anyone.

NOAA, Capt. Budd Christman

A humpback whale.

A: Many marine animals drown as the final part of dying, says Dr. Bruce Mate,
Director of the Endowed Marine Mammal Program at Oregon State University, who
has been studying marine mammals for 31 years. Drowning is usually a secondary
effect much like people dying of pneumonia when gravely ill.

Healthy marine mammals, however, don't struggle to reach the surface to breathe.
They evolved positive or neutral buoyancy and live effortlessly near the sea
surface, even while sleeping. Yet, they are air-breathing
animals and, when their health fails, "are prone to drowning," agrees Dave Rugh,
wildlife biologist at the U.S. National Oceanic and Atmospheric Administration's
(NOAA) National Marine Mammal Laboratory in Seattle.

Seals, sea lions, and fur seals frequently come ashore when they are sick,
where they can rest, recover, and save themselves.

This strategy, on the other hand, misfires for whales. Often, says Mate, we
find sick whales ashore, who may have beached themselves to avoid drowning.
Before they can recover, though, gravity pools their blood or they overheat
enough to cause irreversible tissue damage. They die soon  even if people
push them back into the water.

As far as holding their breath forever, this does happen but only extremely
rarely. "The behavior," says NOAA marine biologist Richard Merrick, "is so powerful
that if triggered out of the water by handling or stress, individuals can stop
breathing and asphyxiate (though surrounded by air)."